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Surface Water Management

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Surface Water Management

As part of Guernsey Water’s 10 year Business plan, outcomes aim to deliver effective drainage and protect the island’s environment by reducing the risk of sewer flooding and pollution whilst being more sufficient and resilient.

Flood and Pollution Risk

The island’s sewer network conveys waste water to Belle Greve Wastewater Centre and in many locations, also collects rainwater from roof and road drainage. The capacity of the network can be exceeded in rain events where the rain runs off vast areas of impermeable surfaces into the sewer network can cause diluted spills into the coastal waters via our combined sewer overflows to prevent flooding. In more extreme events, flooding is experienced, causing loss of service and damage.

Future Challenges

Rainfall runoff is hard to manage as the impact has increased due to new developments (often over previously Greenfield land) and urban creep (the extensions to existing properties and paving of driveways that increases the speed of runoff into the sewers) which are exacerbated by climate change. Furthermore, once storm water enters the network it becomes a burden for Guernsey Water to pump, treat and dispose of. By contrast, in its natural state the rainwater would have made its way instead to groundwater, surface water bodies and the sea without any requirement for human intervention.

A Sustainable Approach

The removal or attenuation of surface water from the sewage system reduces this risk as well as creating headroom for predicted further development to occur on island. Traditional storage tank solutions are expensive, often limited by space, can leave long term legacies of operation and maintenance and require upsizing as volumes increase. The most effective way of adapting to this over the long-term will be through managing storm water using sustainable drainage systems (SuDS). Sustainable Drainage Systems aim to mimic natural water management practices and are designed to drain surface water in a manner that will provide a more sustainable approach than the conventional practice of routing run-off through a pipe to a watercourse, in order to reduce risk of flooding. Guernsey Water are actively promoting the use of sustainable drainage on all sites and in particular scenarios to existing infrastructures.


For a full copy of the Surface Water Management Policy, click here


From Twitter

RT @LesVoiesSchool: Great trip to Kings Mills Water treatment works this week with Middle School – thanks @Guernseywater https://t.co/AZkj8
There is a water reservoir floating in space that is equivalent to 140 trillion times all the water in the world's… https://t.co/Ri4rQDBsMh
Our Surface Water Management Policy endorsed by @Govgg Committee for Environment & Infrastructure can be found here… https://t.co/4HrkeWDuoy
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